I think you can get the NAV without controlled airspace but you do need the radio endorsement which basically comes with your RAA training. The english test i believe is needed for controlled airspace.
Cost is all relative as flying is all competency based. I did RPC in 20.5 Hours (i think 20 is min). Navs i have done 2x with instructor 1x solo and now up to the flight test each averages around 3-4 hours but depends on school and location. Each hour is about $230ph (i won't add it up i don't want to know) Can rent for as low as $189ph
endorsements Radio, Pax, NW, HF
With the hours above though i have seen people do it quicker and others do it much slower due to competency.
But the trick is don't count the total cost like any hobby you do it slowly and fly because you enjoy and don't count the $$$